Question: Sudden increase in vibration per watt in a 12MW steam turbine

Thread Content

A Hangzhou Steam Engine Company extraction-type condensing steam turbine: the vibration of shaft 1 is X 37μm and Y 26μm; the vibration of shaft 2 is X 50μm and Y 72μm. After extraction, the vibration of shaft 2 increases to X 67μm and Y 116μm. There is no change when the load is increased or decreased, and all measurement points show normal values; the casing vibration is 20μm, which is within acceptable limits； Half a month later, with a load of 9,000 KW, the displacement increased from 0.19 to 0.31 mm after 9S; the variation increased from -0.53 to 0.2 mm. The shaft vibration for axis 1 increased from 37 to 174 μm in the X direction and from 26 to 216 μm in the Y direction, while the shaft vibration for axis 2 decreased from 63 to 47 μm in the X direction and from 116 to 72 μm in the Y direction, resulting in a sequential trip of the machine. After checking that the unit was in good condition, it was restarted under load. The shaft vibration for bearing 1 was X 37μm and Y 30μm, while for bearing 2 it was X 65μm and Y 110μm. Why did this situation occur?